Childhood obesity is one of our nation's most significant public health problems. Hispanic youth are particularly at risk and are more likely to be overweight and obese than their non-Hispanic white counterparts partly because of their inadequate levels of physical activity and the poor quality of their dietary intake. Family functioning, specifically parental involvement and family communication, is related to a number of health behaviors and conditions, including drug use, tobacco use, sexual risk behaviors, physical activity, dietary intake, and body mass index (BMI). Despite the evidence that parental involvement and parent- adolescent communication have a role in obesity prevention, their incorporation into obesity prevention interventions has been limited. Thus, there is a critical need to develop family-based obesity preventive interventions for youth that target physical activity and poor diet, especially for Hispanic youth -- given the disproportionate and multiple obesity-related health burdens they face. Familias Unidas (United Families in English) is a family-based, culturally-specific intervention found to be efficacious in preventing or reducing a number negative health behaviors and conditions, including drug use, alcohol use, depression, sexual risk behaviors, conduct problems, sexually transmitted diseases, and alcohol dependence. Familias Unidas has impacted these outcomes through improvements in family functioning (e.g, parental involvement and parent-adolescent communication), the same mechanism that has been found to be related to physical activity and dietary intake. Preliminary data also indicate that Familias Unidas has positive effects on physical activity and that the effects of the intervention on physical activity are partially mediated by parental involvement. This study's aims are: AIM 1: To examine the relative efficacy of Familias Unidas, extended to target obesity, in increasing physical activity and improving the quality of dietary intake among overweight Hispanic youth and AIM 2: To examine whether and to what extent family functioning partially mediates the effects of Familias Unidas on physical activity and quality of dietary intake. To achieve these aims the proposed study will randomize 280 Hispanic youth to one of two conditions: 1) Familias Unidas or 2) a community practice control condition. Three study hypotheses will be tested: H1: Familias Unidas will be efficacious, compared to Community Practice, in increasing Hispanic youth's past seven day moderate to vigorous physical activity over time; H2: Familias Unidas will be efficacious, compared to Community Practice, in improving Hispanic youth's past seven day quality dietary intake (defined as decreases in sugar-sweetened beverages, decreases in intake of fast foods, and increases in fresh fruits and vegetables) over time; and H3: Familias Unidas' effects on youth's past day moderate to vigorous physical activity and youth's past seven day quality dietary intake will be partially mediated by changes in family functioning over time.